(function flexible (window, document) {
  var docEl = document.documentElement
  var dpr = window.devicePixelRatio || 1

  // adjust body font size
  function setBodyFontSize () {
    if (document.body) {
      document.body.style.fontSize = (12 * dpr) + 'px'
    } else {
      document.addEventListener('DOMContentLoaded', setBodyFontSize)
    }
  }
  setBodyFontSize()

  // set 1rem = viewWidth / 10
  function setRemUnit () {
    // var rem = docEl.clientWidth / 10
    // docEl.style.fontSize = rem + 'px'

    var width = docEl.getBoundingClientRect().width
    // 当屏幕超过1920px以后就不在随着屏幕的变大而变大了
    if (width / dpr > 1920) {
      width = 1920 * dpr
    }
    // 当屏幕小于1300px以后就不再随着屏幕的变小而变小了
    // if (width / dpr < 1300) {
    //   width = 1300 * dpr
    // }
    var rem = width / 19.2
    docEl.style.fontSize = rem + 'px'
    window.rem = rem
  }

  setRemUnit()

  // reset rem unit on page resize
  window.addEventListener('resize', setRemUnit)
  window.addEventListener('pageshow', function (e) {
    if (e.persisted) {
      setRemUnit()
    }
  })

  // detect 0.5px supports
  if (dpr >= 2) {
    var fakeBody = document.createElement('body')
    var testElement = document.createElement('div')
    testElement.style.border = '.5px solid transparent'
    fakeBody.appendChild(testElement)
    docEl.appendChild(fakeBody)
    if (testElement.offsetHeight === 1) {
      docEl.classList.add('hairlines')
    }
    docEl.removeChild(fakeBody)
  }
}(window, document))
